Ultimate analyzer, scanning transmission electron microscope and ultimate analysis method

ABSTRACT

An object of the present invention is to provide an ultimate analyzer which can display an element distribution image of an object to be analyzed with high contrast to determine the positions of the element distribution with high accuracy, and a scanning transmission electron microscope and a method of analyzing elements using the ultimate analyzer. The present invention exists in an ultimate analyzer comprising a scattered electron beam detector for detecting an electron beam scattered by an object to be analyzed; an electron spectrometer for energy dispersing an electron beam transmitted through the object to be analyzed; an electron beam detector for detecting said dispersed electron beam; and a control unit for analyzing elements of the object to be analyzed based on an output signal of the electron beam detected by the electron beam detector and an output signal of the electron beam detected by the scattered electron beam detector. Further, the present invention exists in a scanning transmission electron microscope comprising the above ultimate analyzer; an electron beam source; an electron beam scanning coil; a scattered electron beam detector; objective lenses; a focusing lens; a magnifying magnetic field lens; and a focus adjusting electromagnetic lens. Furthermore, the ultimate analyzer or the scanning transmission electron microscope may comprises a control unit which makes it possible that both of an image of element distribution and an STEM image detected and formed by the scatted electron beam detector are observed at a time in real time, and the image of element distribution is corrected by the STEM image detected and formed by the scattered electron beam detector.

This is a continuation-in-part of U.S. patent application Ser. No.10/069,793, filed Apr. 3, 2002 which is a 371 of Application No.PCT/JP01/09618 on Nov. 2, 2001, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a novel ultimate analyzer for analyzingelements of an object to be analyzed based on an output signal of ascattered electron beam and a plurality of output signals of an electronbeam energy dispersed after passing through an object to be analyzed,and a scanning transmission electron microscope having the ultimateanalyzer and an ultimate analysis method using the scanning transmissionelectron microscope.

With progressing of miniaturizing and downsizing of semiconductordevices and magnetic head elements, the structure of these elements hasa structure that thin films of several nm (nanometers) are laminated inan area of a sub-micrometer order. Since the characteristics of thesemiconductor elements and the magnetic head elements strongly depend onthe structure, the element distribution and the crystal structure insuch a micro-area, it is important to analyze them in the micro-area.

As the means for observing a micro-area, there are a scanning electronmicroscope (SEM), a transmission electron microscope (TEM) and ascanning transmission electron microscope (STEM). Only the TEM and theSTEM have a spatial resolution of a nanometer level. The TEM is anapparatus in which an electron beam is irradiated onto a sample, and thetransmitted electron beam is magnified using a lens. On the other hand,the STEM is an apparatus in which an electron beam is focused onto amicro-area, and a two-dimensional image is obtained by measuringintensities of the transmitted electron beam while the electron beam isbeing scanned on the sample.

As the means for observing a two-dimensional distribution of elements ona plane of a sample, there are an energy dispersive X-ray spectroscopy(EDX) and an electron energy loss spectroscopy (EELS) using the TEM orthe STEM. For example, in a case of analyzing a metal film, Cr, Mn, Fe,Co, Ni and Cu can be identified using the energy dispersive X-rayspectroscopy, and two-dimensional distributions of the above metals canbe obtained.

On the other hand, by using the electron energy loss spectroscopy,silicon, oxygen and nitrogen can be identified, and two-dimensionaldistributions of silicon, silicon oxide and silicon nitride can beobserved. The electron energy loss spectroscopy is a method of analyzinglost energy for exciting inner-shell electrons of elements composing asample when the electron beam transmitting through the sample. Theelectron that lost energy due to the excitation of the inner-shell ofthe element to be analyzed is called as core-loss electron. The ultimateanalysis can be performed because the lost energy is specific to anelement, and a two-dimensional distribution of the elements can beobserved by performing energy analysis in each position in the plane ofthe sample. These spectroscopy are widely used by combining the STEM anda parallel detection type electron beam energy loss spectrometer.

The parallel detection type electron beam energy loss spectrometercomprises a magnetic-prism spectrometer; quadrupole electromagneticlenses and hexapole electromagnetic lenses arranged at the front of andat the rear of the magnetic-prism spectrometer; and a parallel detectorarranged after the magnetic-prism spectrometer. The quadrupoleelectromagnetic lenses are used for adjusting focus of the electronenergy loss spectra and for magnifying the electron energy loss spectra.The hexapole electromagnetic lens is used for reducing aberration of theelectron energy loss spectra projected on the detector. The electronenergy loss spectra magnified by the quadrupole electromagnetic lens isprojected on the parallel detector to measure a wide range of theelectron energy loss spectra.

The prior art in regard to the structure of the parallel detection typeelectron energy loss spectrometer is disclosed in, for example, U.S.Pat. No. 4,743,756, Japanese Patent Application Laid-Open No. 7-21966,Japanese Patent Application Laid-Open No. 7-21967, and Japanese PatentApplication Laid-Open No. 7-29544. An electron energy analyzer isdisclosed in Japanese Patent Application Laid-Open No. 57-80649.

In a conventional apparatus combining the parallel detection typeelectron energy loss spectrometer and the STEM, a user performs (1)specifying a measured position, (2) specifying an element, (3) measuringan energy intensity distribution of the electron beam using the electronbeam detection part, (4) correcting background of the detection part andcorrecting the gain of the detection part, (5) specifying a backgroundregion of the spectrum, (6) specifying a background fitting functionsuch as the power-low model (I=A×E⁻¹; A and r are coefficients, and E isenergy), (7) specifying an integration region of the signal intensity,(8) displaying the signal intensity of the specified element in themeasured position on the image display unit, and (9) performing theoperation of the item (1). Since it is necessary to perform therepetitive operation described above for all the measuring points, ittakes a long time to obtain a two-dimensional image, and accordingly itis difficult to obtain an element distribution in real time. Further, itcan be considered to obtain the two-dimensional image by the method thatafter measuring the electron energy loss spectra for all the measuredpoints, the user specifies the operations of (2) to (7). In this method,the volume of measured data becomes very large, and further, the elementdistribution image can not be obtained in real time.

In addition to the above, in the case where the element distributionimage can not be obtained in real time, there are following problems:

(A) In a case where analysis of an interface between thin films, theanalysis region (the interface between thin films) can not be identifiedby using a TEM/STEM image when measuring the electron energy lossspectra. Accordingly, whether or not the region to be measured isincluded in the analyzed region cannot be judged until the elementdistribution image is obtained after analyzing the electron energy lossspectra.

(B) The conventional analyzer is not suitable for the work such as theinspection to measure many samples because it requires the measurementof the electron energy loss spectra and the many complicated and complexoperations for each measured point, and also it requires a long time forthe measurement and the analysis.

(C) In a case of identifying an oxide film or a deposited element formedin an interface between dissimilar metals, it cannot be identified byobserving only a distribution image of the single element which metalbetween the dissimilar metals is oxidized, or it is difficult to beidentified by observing the element distribution image whether theelements exist on the interface between the dissimilar metals or aredistributed inside one of the metals.

Further, in an analyzer which detects an element to be analyzed bydividing an intensity of a first electron beam in an energy rangecontaining a core-loss peak among the electron energy loss spectra ofthe element to be measured by an intensity of a second electron beam inan energy range higher than the core-loss peak, which is called as ajump-ratio method, there is the following problem depending on thesample to be analyzed.

When light elements such as oxygen, nitrogen and the like are observedin a case where a heavy metal element exists in the sample to bemeasured, a portion of the heavy metal element is sometimes displayedwith brightness similar to brightness of the distribution image of thelight elements. In that case, since the contrast difference between ametal portion and an oxide or nitride portion becomes small, it becomesdifficult to judge correctly existence of oxide or nitride.

As described above, the analyzer combining the electron energy lossspectrometer and the STEM is difficult to observe an elementdistribution image having high contrast in real time and to determinethe distribution of the element with high accuracy.

On the other hand, as a means for preventing degradation of an image dueto brightness variation of an electron source in STEM image observationusing a scanning transmission electron microscope, Japanese PatentApplication Laid-Open No. 2000-21346 discloses a scanning transmissionelectron microscope in which one of an output signal from a detectingmeans for detecting transmission electrons transmitted through a sampleand an output signal from a detecting means for detecting scatteredelectrons scattered by the sample is divided by the other. However, thispatent discloses a means for improving image quality of a STEM image,but not a means for analyzing elements of the sample.

The literature by K. Kaji, et al., “Light Element Mapping Method withScanning Transmission Electron Microscope”, The Japanese Society ofElectron Microscopy, May 17, 2000: p307, describes a method forobtaining an oxygen distribution image, in which gate electrodes aredark and oxidized films thereon are bright.

According to the description, using a transmission electron scanningmicroscope of a field-emission type and an ultimate analyzingobservation apparatus, the method obtains such image by logical dividingoperation applied to an oxygen distribution image acquired by 2-windowmethod using a Z-contrast image as the divisor.

However, this method is still not enough to respond to the demand formore contrasted screen-displaying of gate electrodes and oxidized filmsthereon.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide an ultimate analyzerwhich can display an element distribution image of an object to beanalyzed with high contrast to determine the positions of the elementdistribution with high accuracy, and a scanning transmission electronmicroscope and a method of analyzing elements using the ultimateanalyzer.

The present invention is characterized by an ultimate analyzercomprising a control unit for detecting an element of an object to beanalyzed based on an output signal of an electron beam detector bydispersing an electron beam transmitted through a sample, particularly,based on an intensity of the output signal and an output signal of aring-shaped scatted electron beam detector for detecting an electronbeam scattered by the sample.

Further, the present invention is characterized by an ultimate analyzercomprising an image display unit for displaying an element distributionimage of an object to be analyzed obtained based on an intensity of anelectron beam detected by an electron detector passing through a sampleand being dispersed; and an element distribution image of the object tobe analyzed obtained based on an intensity of an electron beam detectedby the scattered electron beam detector described above.

Further, the present invention is characterized by an ultimate analyzercomprising any one of an image display unit for displaying line profilesof an element of the object to be analyzed obtained from an analysisresult output from a control unit for analyzing the element of theobject to be analyzed based on an intensity of the dispersed electronbeam detected by the electron beam detector and an analysis resultoutput from the control unit for analyzing the element of the object tobe analyzed based on an intensity of the electron beam detected by thescattered electron beam detector, and an image display for displaying adistribution image of the element, and an image display unit fordisplaying the distribution image of the element and a distributionimage of the element based on the intensity of the electron beamdetected by the scattered electron beam detector with two image planesside-by-side at a time or with sequential one-image planes or with twoimage planes overlapped with each other. The output signal detected bythe electron beam detector is expressed by the intensity, but theelectron beam detector detects an amount of electrons.

Further, the present invention is characterized by a scanningtransmission electron microscope comprising an electron beam source forgenerating an electron beam; an electron beam scanning coil; a scatteredelectron beam detector for detecting a scattered electron beam scatteredby an object to be analyzed; an objective lens for condensing theelectron beam on the object to be analyzed; a focusing lens; amagnifying magnetic field lens; a focus adjusting electromagnetic lens;a scanning portion for scanning the electron beam; an electrondispersing portion for energy-dispersing the electron beam; and anelectron beam detector portion for detecting part or all of the electronbeam energy-dispersed by the electron dispersing portion, whichcomprises the ultimate analyzer described above.

That is, the present invention is characterized by a scanningtransmission electron microscope comprising a processor for performingoperation using only an intensity of an electron beam detected by theelectron beam detector for detecting at least part of the electron beamdispersed by the electron dispersing portion or using both of theintensity of the electron beam and a result of an intensity of anelectron beam detected by the scattered electron beam detector, anddisplays the operated result of the processor at the same time or inparallel with scanning the electron beam using the scanning portion orafter the electron beam scanning. Further, the present invention ischaracterized by that an image based on the electron beam intensitydetected by the scattered electron beam detecting portion is displayedtogether with the operated result of the processor side-by-side oroverlapping with each other. Therefore, by the analyzer combining anelectron energy loss spectrometer and an STEM, an element distributionimage can be displayed on a screen in real time.

Further, the present invention is characterized by a scanningtransmission electron microscope comprising the dispersing conditions ofthe electron beam losing energy due to the excitation of the inner-shellelectron in the element to be analyzed; and two or more channels ofelectron beam detecting portions for detecting dispersed electron beams,wherein the ultimate analysis is progressed by specifying a element tobe observed after specifying a measurement region; then obtaining energydispersing conditions of core-loss electrons of the specified elementfrom a dispersing condition memory unit; automatically adjusting theelectron optical system of the electron dispersing portion and theelectron beam detecting portion so that the core-loss electrons may bedetected; measuring an intensity of the core-loss electrons and anintensity of electrons just lower than the energy of core-loss electronsby the electron beam detecting portion using at least one channel foreach while the electron beam is being scanned using the scanningportion; performing background correction and gain correction of theelectron beam detecting portion using the processor; executingoperation, preferably, dividing an intensity of an electron beam of thecore-loss edge in an electron energy loss spectrum by the intensity ofan electron beam just before the core-loss edge; and displaying both ofthe operated result obtained by the division and the result based on theintensity of the electron beam detected by the scattered electron beamdetector on the image display unit at a time or in parallel oroverlapped with each other in real time.

Further, the scanning transmission electron microscope in accordancewith the present invention is characterized by that the operated resultobtained by dividing the intensity of an electron beam includingcore-loss electrons by the intensity of an electron beam whose energy issmaller than the energy of core-loss electrons is operated using theintensity of the electron beam detected by the scattered electron beamdetecting portion, and the operated result obtained as the result isdisplayed solely or together with side-by-side or overlapped with animage based on the intensity of the electron beam detected by thescattered electron beam detecting portion on the image display unit inreal time. When an image is formed by electrons scattered by a sample ina high angle using the scattered electron beam detecting portion, theobtained image is also called as a Z-contrast image.

The present invention is characterized by an ultimate analyzer which canobserve and display an element distribution image and a Z-contrast imageat a time in real time during scanning the electron beam, and canobserve an element distribution image corrected by the Z-contrast image.

The present invention is characterized by an ultimate analysis methodcomprising the steps of detecting an output signal of an electron beampenetrated through an object to be analyzed, preferably as an intensityfor each energy of the electron beam; and analyzing an element,preferably a non-metallic element, of the object to be analyzed based onan output signal of the detected electron beam, wherein the intensity ofthe output signal is corrected by an output signal, preferably by anintensity, of the electron beam scattered by the object to be analyzed.

Further, the present invention is characterized by that in the electronenergy loss spectrum obtained by dispersing energy of an electron beampenetrated through an object to be analyzed, analysis of element of theobject to be analyzed obtained by operating based on both an intensityof an electron beam within an energy range including a core-loss edgeappearing in the electron energy loss spectrum by electrons exciting theinner-shell electron of an element composing the object to be analyzedand an intensity of an electron beam having a higher energy than thecore-loss edge or the element analysis image are obtained by correctingthe intensity of the electron beam scattered by the object to beanalyzed.

Further, the present invention is characterized by that in an ultimateanalysis method comprising the steps of detecting an intensity of anelectron beam penetrated through an object to be analyzed; analyzing anelement of the object to be analyzed based on the intensity andloss-energy of the detected electron beam; and displaying an image ofthe ultimate analysis on a screen, wherein the image of the ultimateanalysis is displayed on the screen by being corrected by a Z-contrastimage obtained from operation based on an intensity of an electron beamscattered by the object to be analyzed.

The present invention is to provide an ultimate analyzer comprising: acontrol unit for analyzing elements of said object to be analyzed basedon a computed output signal obtained either through adding orsubtracting operation applied between an intensity of a transmittedelectron beam and an intensity of a scattered electron beam or throughdividing operation applied to said transmitted beam intensity using thesquare root of said scattered beam intensity as the divisor; and acomputing unit either for adding or subtracting operation between theintensity of said transmission electron beam and the intensity of saidscattered electron beam or for dividing operation to said transmissionbeam intensity using the square root of said scattered electron beamintensity as the divisor; and a screen-display device for the correctedimage of the analyzed results.

Another feature of the present invention is to provide a method forultimate analysis comprising the steps of: correcting an image based ona computed output signal obtained either through adding or subtractingoperation applied between an intensity of a transmitted electron beamand an intensity of a scattered electron beam or through dividingoperation applied to said transmitted beam intensity using the squareroot of said scattered beam intensity as the divisor; and displaying thecorrected image on a screen.

Said ultimate analysis image and a Z-contrast image may be displayed inany of styles: a side-by-side shared-screen assignment for said analysisimage and said Z-contrast image, another side-by-side shared-screenassignment for said Z-contrast image and a processed image obtained bylogically dividing said analysis image by said Z-contrast image, aswitching display wherein said analysis image or said Z-contrast imageappears by switching, or superimposed display of said ultimate analysisimage and said Z-contrast image each being given contrast gradation withcolors other than black and white but different each other.

On every electron beam position irradiated onto a specimen, the ultimateanalysis result obtained through EELS spectrum or the same but obtainedthrough EELS spectrum and said Z-contrast image is displayed. This meansthat the line profile is displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) are schematic block diagrams showing the main portionof a scanning transmission electron microscope having an ultimateanalyzer in accordance with the present invention;

FIG. 2 is a graph showing an example of an electron beam energy lossspectrum of the core-loss electrons;

FIGS. 3(a) and (b) are STEM photographs showing an oxygen distributionimage near a gate electrode of a semiconductor element and an oxygendistribution image obtained by dividing the oxygen distribution image byan electron beam intensity of a scattered electron beam detector;

FIGS. 4(a) and (b) are STEM photographs showing a nitrogen distributionimage near the electrode of a semiconductor element and a nitrogendistribution image obtained by dividing the nitrogen distribution imageby an electron beam intensity of a scattered electron beam detector; and

FIGS. 5(a) and (b) are STEM photographs showing an oxygen distributionimage near the electrode of a semiconductor element and an oxygendistribution image obtained by subtracting the oxygen distribution imagethat was obtained by operating based on the an electron beam intensityof a scattered electron beam detector. FIGS. 5(c) and (d) show aZ-contrast image and a superimposition display, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram showing the main portion of ascanning transmission electron microscope (hereinafter, referred to asan electron microscope) having an embodiment of an ultimate analyzer inaccordance with the present invention. FIG. 1(a) is a front view, andFIG. 1(b) is a view (a top view) seeing FIG. 1(a) from an electron beamsource 1. In this figure, the portion from the electron beam source 1 toa phase contrast detector 22 is indicated as the mainframe of theelectron microscope. The mainframe of the electron microscope includes acomponent for controlling scanning of an electron beam, not shown, usedfor exerting the function as the electron microscope.

Further, the portion from a scattered electron beam detector 21 to anelectron beam detector 13 is indicated by an ultimate analyzer. A signalto a control unit 26 and a signal from the control unit 26 aretransmitted through a signal line 103. An input unit such as a keyboardand so on and a processor 23, a memory unit 24, and an image displayunit 25 are connected to the control unit 26. A dispersing condition ofCore-loss edge and plasmon energy for an element are stored in thememory unit 24. On the image display unit 25, an intensity of theelectron beam detected by a secondary electron detector 20 and/or anintensity of the electron beam detected by the scattered electrondetector 21 or a operated result of the processor 23 and a element to beanalyzed specifying button capable of specifying two or more kinds ofelements to be analyzed while the electron beam is being scanned aredisplayed.

The scattered electron beam detector 21 is of a ring-shape having adesired diameter, and detects the electron beam scattered by an elementcomposing a semiconductor device or a magnetic head element by the wholecircumference of the ring. Thereby, the scattered electron beam detectorcan detect the element with a high accuracy, and in order toappropriately detect the scattered electron beam, the intensity of theincident electron beam is controlled so that the scattered electron beammatches the diameter of the detector. Further, in order to form a highcontrast image display, it is preferable to detect an elementcorresponding to an element to be displayed by arranging a plurality ofscattered electron beam detectors 21 in the vertical direction or thetransverse direction, as to be described later.

The electron beam 2 generated in the electron beam source 1 is deflectedby an electron beam scanning coil 3. The deflected electron beam 2 isconverted on the plane of a sample 5 by upper magnetic field 4 of anobjective lens to be irradiated on the sample 5. Secondary electronsemitted from the sample are detected by a secondary electron detector20, and the intensity of the detected electron beam is displayed on theimage display unit 25 to observe the secondary electron image. Electronsscattered with a high angle among the electrons scattered by the sampleare detected by a scattered electron beam detector 21, and the intensityof the detected electron beam is displayed on the image display unit 25to observe the Z-contrast image.

The electron beam scattered by and transmitted through the sample formsan object point 10 by an objective lens lower magnetic field 6 and aprojective lens 8. The electron beam having the object point 10 isincident to the ultimate analyzer. A spectrial electron spectrograph 11arranged in the downstream side through a phase contrast detector 22before a focus adjusting electromagnetic lens 16. The magnetic field ofa magnet composing the magnetic-prism spectrometer 11 forms a magneticfield vertical to the plane of paper of FIG. 1. The electron beamincident to the magnetic-prism spectrometer 11 is deflected by 90° andenergy-dispersed, and then focused on an energy dispersed plane 12. Byadjusting the relationship between an output signal obtained by thescattered electron beam detector 21 and an output signal obtained by theelectron beam detector 13 using a value obtained by the phase contrastdetector 22, a high contrast can be formed.

In this embodiment, the spectrum formed on the energy dispersed plane 12is about 1 eV/μm when the radius of rotation of the electron beam of themagnetic-prism spectrometer is 100 mm. In order to make the focus thespectrum magnified by the magnifying magnetic field lens 15 on theenergy dispersing plane 12, the magnetic field of the focus adjustingelectromagnetic lens 16 is adjusted. By doing so, the electron energyloss spectrum 18 projected on the electron beam detector 13 becomes 0.01eV/μm. It becomes 0.25 eV/channel when a multi-channel plate array of 25μm/channel is used as the electron beam detector 13. Since the detectoris formed of 1024 channels, the full range becomes 250 eV.

Further, the electron beam detector 13 may have a structure that aplurality of scintillators having, for example, 2 mm channel width arearrayed in the energy dispersing direction, and light from thescintillators is amplified using a photomultiplier.

A real-time element mapping method using the present embodiment will bedescribed below.

A user should be involved only in (1) a process to specify element, (2)a spectrum checking process and (3) an analysis region specifyingprocess of processing to specify a measurement region. The otherprocesses are executed under control of the control unit 26 to controlthe electron microscope mainframe and the ultimate analyzer.

The ultimate analyzer is constructed so that the zero loss electron beamcomes near the center of the electron beam detector 13. The intensity ofthe electron beam lost above 250 eV as a result of the excitation of theinner-shell electron is measured by accelerating the electron beam usingan accelerating tube 19 arranged inside the magnetic-prism spectrometer11. When the intensity of the electron beam lost above 500 eV ismeasured, the loss electrons are accelerated by applying 500 V to theaccelerating tube. By doing so, the loss electron beam required to bemeasured can be shifted to the center of the detector 13.

An element to be analyzed is displayed by buttons each having a name ofelement on the image display unit 25. When an element to be analyzed isspecified using the element specifying button, a dispersing condition ofthe specified element is obtained from the dispersing condition memoryunit 24, and the optical system is adjusted using the magnetic-prismspectrometer 11 of the ultimate analyzer and the accelerating tube 19arranged in the magnetic-prism spectrometer, the magnification magneticfield lens 15, the focus adjusting magnetic field lens 16 and so on toperform element mapping. Further, by performing the above-describedoperation during scanning the electron beam, it is possible to performmapping of two or more kinds of elements in real time by switching theelement to be analyzed. The various kinds of images measured asdescribed above are displayed on the image display unit 25.

FIG. 2 is a graph showing a shape of an electron beam energy lossspectrum obtained by exciting inner-shell electrons of an elementcomposing an object to be measured. When an electron beam is incident toa sample, electrons among the incident electrons lose energy specific toan element of the sample by exciting the inner-shell electron of theatom. The inner-shell electron exciting electron means the electron listits energy. As shown in FIG. 2(a), in a case where a spectrum showingthe core-loss edge is measured by individually setting a range justbefore the core-loss edge 27 (pre-window 28) and a range including thecore-loss edge (post-window 29) as one window, respectively, (2-windowmethod), it is necessary to determine an energy width of the window andan energy width between the two windows. In the present embodiment, theoperation is automated by storing the relating information in the memoryunit 24.

The memory unit 24 stores the core-loss edge energy (eV), conditions ofwindow width (energy width, or number of channels) and gap betweenwindows (energy width, or number of channels), condition of the focusadjusting magnetic field lens 16, and condition of the magnifyingmagnetic field lens 15 for each element. When a user specifies anelement to be analyzed, a voltage corresponding to the core-loss edgeenergy is applied to the acceleration tube 19, and an optimum current isconducted to each of the focus adjusting magnetic field lens 16 and themagnifying magnetic field lens 15, and a window width and a window gapare given by the memory unit 24. The electron beam intensities obtainedfrom the two windows are corrected their backgrounds and gains specificto the detector in the processor 23, and then the intensity ratio of thetwo windows is operated and displayed on the image display unit 25. Inthis case, by outputting the control signal 101 from the control unit 26to the electron microscope mainframe through the signal line 103 toperforming the processing linking with the electron beam scanning coil3, an element distribution image can be obtained in real time. By thismethod, the element distribution image can be obtained in a shortprocessing time.

In the case of the two-window method, for example, in the electronenergy loss spectrum 27 caused by the excitation of oxygen K-shellelectron shown in FIG. 2, an oxygen distribution image can be obtainedby dividing the electron beam intensity of the post-window 29 by theelectron beam intensity of the pre-window 28. An electron energy lossspectrum 50 for a metal element is also shown in FIG. 2. However, whenthe electron beam intensity of the post-window 29 is divided by theelectron beam intensity of the pre-window 28 in a case where thegradient of the electron energy loss spectrum 50 is small, the dividedresult sometimes becomes nearly equal to a divided result of the oxygencase. In such a case, a portion where oxygen does not actually exist (inthis case, for example, a portion where a metallic element exists) showsbright contrast in an image observing oxygen distribution, andaccordingly the oxygen distribution image has a small contrastdifference to the metallic element portions.

In this case, processing of operating the element distribution imageoperated according to the two-window method using the electron beamintensity from the scattered electron beam detector 21 is selected, andoperation is executed linking with the scanning coil 3. The operationexecuted here is to divide the element distribution image by theelectron beam intensity from the scattered electron beam detector 21, orto divide the element distribution image by the square root of theelectron beam intensity from the scattered electron beam detector 21, orto subtract the electron beam intensity obtained from the scatteredelectron beam detector 21 from the signal intensity expressing theelement distribution image. An image obtained from the scatteredelectron beam detector is also called as a Z-contrast image, and theZ-contrast image depends on an atomic number of an element, and thecontrast becomes brighter as the atomic number becomes larger.Therefore, by dividing the element distribution image obtained throughthe two-window method by the electron beam intensity from the scatteredelectron beam detector 21 or by the square root of the electron beamintensity from the scattered electron beam detector 21, or bysubtracting the electron beam intensity obtained from the scatteredelectron beam detector 21 from the signal intensity expressing theelement distribution image, the contrast in the metal portion becomessmaller than the contrast in the oxygen portion. By displaying theelement distribution image as described above on the image display unit25, the element distribution image of the element to be analyzed can begiven with high contrast.

FIG. 3 is STEM photographs showing an oxygen distribution image near agate electrode of a semiconductor device and an oxygen distributionimage obtained by dividing the oxygen distribution image by an electronbeam intensity of the scattered electron beam detector. The STEMphotographs are results of observing a section near the electrode usingtungsten as a metallic element for the electrode material. FIG. 3(a) isthe element distribution image of oxygen observed by the two-windowmethod. An element separation portion 201 is formed of a silicon oxidefilm, and the portion is in a bright contrast in the oxygen distributionimage of FIG. 3(a). However, the gate electrode portion 202 is alsobright. FIG. 3(b) is the result of dividing the oxygen distributionimage of FIG. 3(a) by the electron beam intensity detected by thescattered electron beam detector at the same time of observing theoxygen distribution image. Although the contrast of the elementseparation portion 201 is bright similarly to that in FIG. 3(a), thecontrast of the gate electrode portion 202 becomes dark. Accordingly, ahigh contrast oxygen distribution image excluded the effect of themetallic element can be obtained. The both of the photographs can bedisplayed in one screen on the image display unit 25 side-by-side. Aplurality of image display units 25 may be used to separately displaythe photographs on the image display units one-by-one. By doing so,comparison between the both can be made clearer. Further, different fromthe above, both of the photographs may be colored and displayedside-by-side similarly to the above or overlapping with each other. Bydoing so, the display can be made clearer than the white-and-blackdisplay.

FIG. 4 is STEM photographs showing a nitrogen distribution image nearthe gate electrode of a semiconductor device and a nitrogen distributionimage obtained by dividing the nitrogen distribution image by anelectron beam intensity of a scattered electron beam detector. The STEMphotographs are results of observing a section near the electrode usingtungsten as a metallic element for the electrode material. FIG. 4(a) isthe element distribution image of nitrogen observed by the two-windowmethod. It can be understood that a silicon nitride film 211 is in abright contrast in the nitrogen distribution image of FIG. 4(a).However, the electrode portion 212 is also bright. FIG. 4(b) is theresult of dividing the nitrogen distribution image of FIG. 4(a) by theelectron beam intensity detected by the scattered electron beam detectorat the same time of observing the oxygen distribution image. Althoughthe contrast of the silicon nitride film 211 is bright similarly to thatin FIG. 4(a), the contrast of the electrode portion 212 becomes dark.Accordingly, a high contrast nitrogen distribution image excluded theeffect of the metallic element can be obtained.

Similarly to FIG. 3, the both of the photographs of FIG. 4 can bedisplayed in one screen on the image display unit 25 side-by-side. Aplurality of image display units 25 may be used to separately displaythe photographs on the image display units one-by-one. By doing so,comparison between the both can be made clearer. Further, different fromthe above, both of the photographs may be colored and displayedside-by-side similarly to the above or overlapping with each other. Bydoing so, the display can be made clearer than the white-and-blackdisplay.

FIG. 5 is STEM photographs showing an oxygen distribution image near theelectrode of a semiconductor device and an oxygen distribution imageobtained by subtracting the an electron beam intensity of a scatteredelectron beam detector from the oxygen distribution image the anelectron beam intensity of a scattered electron beam detector. The STEMphotographs are results of observing a section near the electrode usingtungsten as a metallic element for the electrode material. FIG. 5(a) isthe element distribution image of oxygen observed by the two-windowmethod. It can be understood that a silicon oxide film 221 is in abright contrast in the oxygen distribution image of FIG. 5(a). However,the electrode portion 222 is also bright. FIG. 5(b) is the result ofsubtracting the electron beam intensity detected by the scatteredelectron beam detector at the same time of observing the oxygendistribution image from the oxygen distribution image of FIG. 5(a).Although the contrast of the silicon oxide film 221 is bright similarlyto that in FIG. 4(a), the contrast of the electrode portion 222 becomesdark. Accordingly, a high contrast oxygen distribution image excludedthe effect of the metallic element can be obtained.

FIG. 5(c) is the Z-contrast image observed simultaneously with theelement distribution image shown in FIG. 5(a). This Z-contrast image isdisplayed in red-based contrast gradation. In the displayed image of asemiconductor device, gate electrodes thereof brighten the most andother portions, silicon and oxidized silicon films, are darker than saidelectrode portions. The gate electrode materials in the semiconductordevice under observation are tungsten (atomic number 74), silicon (14),and oxygen (8). Differences in these atomic numbers appear asdifferences in contrast gradation in the Z-contrast image. Displayingimages of the element distribution and the Z-contrast with black andwhite gradation is useful for clearly discriminated indication ofelements.

FIG. 5(d) shows the superimposition display using these two images bygiving different colors to each of them. In the display, the oxygendistribution image is given blue-based gradation and the Z-contrastimage red-based, which are then superimposed to be displayed. As shownin FIG. 5(d), the displayed element distribution image appears in brightblue for not only the oxidized silicon films but also for the tungstenelectrode 222; other parts such as silicon portion however appear in adark gradation. In the Z-contrast image, only the tungsten electrode 222brightens in red but oxidized silicon film and silicon portion 223 dark.When images each of which color is given blue and red respectively aresuperimposed, the oxidized silicon film portion appears in bright blue,the silicon 223 portion in dark blue, and the tungsten electrode portion222 reddish blue or bluish red. This superimposing technique in imagedisplaying for analysis result of these kind realizes that acolor-discriminated indication is practicable in displaying aspects ofoxidized silicon films, the tungsten electrode 222, and silicon portion223, which were not available by individual image display. In thespecification, the red portion is rather bright and the blue portion isdark.

As stated above, a distribution image of nonferrous elements can beobserved in high contrast by adding electron beam intensities of theultimate image analysis and of the Z-contrast image.

Displaying images in other color tones than light and shade gives aclearly discriminating image of element distribution, particularly wheretwo or more elements are involved.

Similarly to FIG. 3, the both of the photographs of FIG. 5 can bedisplayed in one screen on the image display unit 25 side-by-side. Aplurality of image display units 25 may be used to separately displaythe photographs on the image display units one-by-one. By doing so,comparison between the both can be made clearer. Further, different fromthe above, both of the photographs may be colored and displayedside-by-side similarly to the above or overlapping with each other. Bydoing so, the display can be made clearer than the white-and-blackdisplay.

Further, the Z-contrast image and the element distribution imageaccording to the two-window method can be captured at a time insynchronism with scanning of the electron beam. When the elementdistribution image according to the two-window method is corrected bythe electron beam intensity detected by the scattered electron beamdetector, a high accurate and high contrast element distribution imagecan be obtained because no displacement exists between the both images.Further, the element distribution image and the Z-contrast image can beobserved at a time, and the results can be displayed on the imagedisplay unit 25 side-by-side. Particularly, by displaying the elementdistribution image and the Z-contrast image overlapping with each other,which position of a sample structural part an observed position in theelement distribution image corresponds to can be easily determined athigh resolution and with high accuracy.

Further, by operating an element distribution image operated accordingto a three-window method using the electron beam intensity detected bythe scattered electron beam detector, a more contrast enhanced elementdistribution image can be obtained. The three-widow method is a methodthat in an electron energy loss spectrum, an electron beam intensitywithin an energy range including a core-loss edge due to the excitationof inner-shell electron in an observed element is subtracted by anelectron beam intensity of the background portion of the electron energyloss spectrum, and the result is displayed as the element distributionimage.

Further, there are provided a plurality of scattered electron beamdetectors, those have different radius, for detecting scatteredelectrons, and at least one of them is a scattered electron beamdetector specifically designed for detecting heavy elements such asmetals and arranged so as to selectively detect heavy elements havingatomic number larger than that of light elements such as oxygen andnitrogen. An element distribution image of oxygen or the like isobserved by the two-window method and at the same time scatteredelectrons are detected by the scattered electron beam detector for heavyelement, and the result operated by the two-window method is divided bythe electron beam intensity detected by the scattered electron beamdetector for heavy element. The element distribution image operated asdescribed above is an image in which only the heavy element portions areselectively in dark contrast. Accordingly, a light element distributionimage excluded the effect of the metallic element can be obtained.

As described in the present embodiment, it is possible to obtain anultimate analyzer capable of observing and displaying an elementdistribution image and a Z-contrast image at the same time in real timeduring scanning the electron beam and also capable of observing anelement distribution image corrected by the Z-contrast image; and ascanning transmission electron microscope comprising the ultimateanalyzer; and a method of analyzing elements using the ultimateanalyzer.

According to the present invention, a light element distribution imageexcluded the effect of the heavy element such as a heavy metal can beobtained by combining the ultimate analyzer and the scanningtransmission electron microscope and correcting an element distributionimage using the electron beam intensity detected by the scatteredelectron beam detector. Therefore, in the present invention, a lightelement distribution image can be observed in high contrast, at highresolution and with high accuracy.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. An ultimate analyzer comprising: a scatteredelectron beam detector for detecting an electron beam scattered by anobject to be analyzed; an electron spectrometer for energy dispersing anelectron beam transmitted through said object to be analyzed; anelectron beam detector for detecting said dispersed electron beam; and acontrol unit for analyzing elements of said object to be analyzed basedon a computed output signal obtained either through adding orsubtracting operation applied between an output signal, or a calculationresult obtained based on said output signal, of the election beamdetected by said electron beam detector and an output signal of thescattered electron beam detected by said scattered electron beamdetector or through dividing operation applied to said output signal orsaid calculation result of said electron beam using the square root ofsaid output signal of said scattered electron beam as the divisor.
 2. Anultimate analyzer comprising: a scattered electron beam detector fordetecting an electron beam scattered by an object to be analyzed; anelectron spectrometer for energy dispersing an electron beam transmittedthrough said object to be analyzed; an electron beam detector fordetecting said dispersed electron beam; an image display unit fordisplaying an element distribution image of said object to be analyzedobtained through computation based on an output signal of the electronbeam detected by said electron beam detector and an element distributionimage of said object to be analyzed obtained through computation basedon an output signal of the electron beam detected by said scatteredelectron beam detector; and a computing unit either for adding orsubtracting operation between the intensity of said dispersed electronbeam, or a calculation result obtained based on said intensity, and theintensity of said scattered electron beam or for dividing operation tosaid intensity of transmission electron beam, or said calculationresult, using the square root of said intensity of scattered electronbeam as the divisor.
 3. An ultimate analyzer comprising: a scatteredelectron beam detector for detecting an electron beam scattered by anobject to be analyzed; an electron spectrometer for energy dispersing anelectron beam transmitted through said object to be analyzed; anelectron beam detector for detecting said dispersed electron beam; anyone of an image display unit for displaying line profiles of an elementof said object to be analyzed obtained from an analysis result outputfrom a control unit for operating the element of said object to beanalyzed based on an output signal of the electron beam detected by saidelectron beam detector and an analysis result output from said controlunit for analyzing the element of said object to be analyzed based on anoutput signal of the electron beam detected by said scattered electronbeam detector, and an image display for displaying a distribution imageof said element, and an image display unit for displaying saiddistribution image of said element and a distribution image of saidelement based on the output signal of the electron beam detected by saidscattered electron beam detector at a time with two image planesside-by-side or sequentially one-image planes or overlapping two imageplanes with each other; and a computing unit either for adding orsubtracting operation between the intensity of said dispersed electronbeam, or a calculation result obtained based on said intensity, and theintensity of said scattered electron beam or for dividing operation tosaid intensity of transmission electron beam, or said calculationresult, using the square root of said intensity of scattered electronbeam as the divisor.
 4. An ultimate analyzer according to any one ofclaims 1 to 3, which comprises an accelerator for accelerating theelectron beam transmitted through said object to be analyzed, whereinsaid control unit controls said accelerator so that said transmittedelectron beam corresponding to the element of said object to be analyzedmay be incident to a fixed position of said electron beam detector, andexecutes operation processing for analyzing the element of said objectto be analyzed based on output signals of the electron beam in aplurality of energy ranges detected by said electron beam detector. 5.An ultimate analyzer according to any one of claims 1 to 3, wherein saidcontrol unit comprises a memory part for pre-storing a value ofacceleration voltage for accelerating said transmitted electron beam andan energy range of said transmitted electron beam for detecting theelement of said object to be analyzed; and an operation part foroperating analysis of the element of said object to be analyzed based onan output signal of the electron beam in said pre-stored energy range,or an intensity of said electron beam and the output signal of theelectron beam detected by said scattered electron beam detector.
 6. Anultimate analyzer according to any one of claims 1 to 3, which analyzesthe element of said object to be analyzed based on output signals of theelectron beam within a plurality of energy ranges among intensities ofsaid dispersed electron beam detected by said electron beam detector orbased on the output signal of said electron beam and the output signalof the electron beam detected by the scattered electron beam detector,and comprises any one of an image display unit for displaying a lineprofile of an element of said object to be analyzed based on the outputsignal of said electron beam relating to said analyzed element and anelectron beam irradiated position in said object to be analyzed; and animage display unit for displaying a distribution image of said element;and an image display unit for displaying said distribution image of saidelement and a distribution image of said element based on the outputsignal of the electron beam detected by said scattered electron beamdetector at a time with two image planes side-by-side or sequentiallyone-image planes or overlapping two image planes with each other.
 7. Anultimate analyzer, according to claim 5, wherein said memory part storescorrecting data for removing an individual influence specific to saidelectron beam detector for detecting said transmitted electron beam, andsaid operating part corrects the output signal of said detected electronbeam based on said correcting data.
 8. An ultimate analyzer according toclaim 5, wherein a first energy range of an energy range including acore-loss edge expressed by a transmitted electron energy loss spectrumrelating to the element of said object to be analyzed arid a secondenergy range of an energy range higher than the core loss energy arepre-stored in said memory part, said control unit controls so as to anoutput signal of a first electron beam detected by an electron beamdetecting portion corresponding to said first energy range and an outputsignal of a second electron beam detected by an electron beam detectingportion corresponding to said second energy range based on said firstenergy range and said second energy range, and said operating partexecute operation processing of the output signal of said first electronbeam and the output signal of said second electron beam, and executesoperation processing of analyzing the element of said object to beanalyzed based on relationship between said operation processed resultand the output signal of the electron beam detected by said scatteredelectron beam detector.
 9. An ultimate analyzer according to claim 8,which comprises an image display unit for displaying said operationprocessed result or an operation processed result based on relationshipbetween said operation processed result and the output signal of theelectron beam detected by said scattered electron beam detector; and theresult based on the output signal of the electron beam detected by saidscattered electron beam detector at a time with two image planesside-by-side or sequentially one-image planes or overlapping two imageplanes with each other.
 10. An ultimate analyzer according to any one ofclaims 1 to 3, which comprises a plurality of said electron beamdetectors for the transmitted electron beam or a plurality of saidscattered electron beam detectors.
 11. An scanning transmission electronmicroscope comprising an electron beam source; an electron beam scanningcoil for scanning an electron beam emitted from said electron beamsource; an upper objective lens for irradiating the emitted electronbeam passed through said coil on a sample; a lower objective lens forcondensing the electron beam coming out from said sample; a scatteredelectron detector for detecting a scattered electron beam among electronbeams transmitted through the sample; a phase contrast detector fordetecting a phase of an electron beam traveling straight among theelectron beams; a lens for focusing the irradiating electron beam; alens for magnifying the electron beam coming out from an electronspectrometer; and an electron beam detector for detecting the electronbeam coming out from said electron spectrometer, which further comprisesan ultimate analyzer for analyzing elements of said sample.
 12. Ascanning transmission electron microscope, comprising an electron beamsource; an electron beam scanning coil for scanning an electron beamemitted from said electron beam source; an upper objective lens forirradiating the emitted electron beam passed through said coil on asample; a lower objective lens for condensing the electron beam comingout from said sample; a scattered electron detector for detecting ascattered electron beam among electron beams transmitted through thesample; a phase contrast detector for detecting a phase of an electronbeam traveling straight among the electron beams transmitted through thesample; a lens for focusing the irradiating electron beam; a lens formagnifying the electron beam coming out from an electron spectrometer;and an electron beam detector for detecting the electron beam coming outfrom said electron spectrometer, which further comprises an ultimateanalyzer for analyzing elements of said sample, wherein said ultimateanalyzer is one of the ultimate analyzer according to claims 1 to
 3. 13.An ultimate analysis method comprising the steps of detecting anelectron beam transmitted through an object to be analyzed; andanalyzing an element of said object to be analyzed based on an outputsignal of the detected electron beam, wherein an intensity of saidoutput signal is corrected by an output signal obtained either fromadding or subtracting operation using the intensity of an electron beamscattered by said object to be analyzed or from dividing operation usingthe square root of the intensity of said scattered electron beam as thedivisor.
 14. An ultimate analysis method comprising the steps ofdetecting an electron beam transmitted through an object to be analyzed;detecting an element of said object to be analyzed based on an outputsignal of the detected electron beam; and displaying an image of saidultimate analysis on a screen, wherein the intensity of said electronbeam or the result of calculation obtained based on said intensity ofelectron beam of said image of said ultimate analysis is corrected by anoutput signal obtained either from adding or subtracting operation usingthe intensity of an electron beam scattered by said object to beanalyzed or from dividing operation using the square root of theintensity of said scattered electron beam as the divisor.
 15. Anultimate analysis method comprising the step of correcting an image ofan ultimate analysis by an output signal obtained either from adding orsubtracting operation using the intensity of an electron beam scatteredby an object to be analyzed or from dividing operation using the squareroot of the intensity of said scattered electron beam as the divisor,said image of said ultimate analysis being obtained from an operationbased on an energy range of core-loss edge expressed an electron energyloss spectrum due to inner-shell electron excitation by an electron beamtransmitted through said object to be analyzed and an energy range justbefore said core-loss edge.
 16. An ultimate analysis method comprisingthe step of analyzing an element of an object to be analyzed based on anenergy range of core-loss edge expressed in an electron energy lossspectrum due to inner-shell electron excitation by electrons transmittedthrough said object to be analyzed and an energy range just before saidcore-loss edge, wherein the intensity of an electron beam or the resultof calculation obtained based on said intensity in said analysis iscorrected by an output signal obtained either from adding or subtractingoperation using the intensity of an electron beam scattered by saidobject to be analyzed or from dividing operation using the square rootof the intensity of said scattered electron beam as the divisor.
 17. Anultimate analysis method comprising the step of displaying an ultimateanalysis image and a Z contrast image on a screen, said ultimateanalysis image being obtained from an operation based on an energy rangeof core-loss edge expressed in an electron energy loss spectrum due toinner-shell electron excitation by electrons transmitted through saidobject to be analyzed and an energy range just before said core-lossedge, said Z-contrast image being obtained from operation based on anintensity of an electron beam scattered by said object to be analyzed.18. An ultimate analysis method comprising the steps of detecting anelectron beam transmitted through an object to be analyzed; analyzing anelement of said object to be analyzed based on an output signal of thedetected electron beam; and displaying an image of said ultimateanalysis on a screen, wherein said image of said ultimate analysis isdisplayed on the screen together with a Z-contrast image obtained fromoperation based on an intensity of an electron beam scattered by saidobject to be analyzed.
 19. An ultimate analysis method comprising thesteps of detecting an electron beam transmitted through an object to beanalyzed; analyzing an element of said object to be analyzed based on anoutput signal of the detected electron beam; and displaying an image ofsaid ultimate analysis on a screen, wherein the intensity of saidelectron beam or the result of calculation obtained based on saidintensity in said image of said ultimate analysis is displayed on thescreen by being corrected either by adding or subtracting operationapplied to the intensity of an electron beam or to the result ofcalculation obtained based on said intensity in a Z-contrast imageobtained from operation based on an intensity of an electron beamscattered by said object to be analyzed or by dividing operation usingthe square root of said output signal as the divisor.